Can’t use `.types`

The Readme says:

> Vantage is an extension of Vorpal, and so inherits all of its properties and methods.

However, I don’t seem to be able to use vorpal’s `types` method as specified [here](https://github.com/dthree/vorpal/wiki/api-|-vorpal.command#commandtypesobject):

```
TypeError: vantage.command(...).description(...).types is not a function
```